This invention is directed toward the preparation of random-fiber thermoset composites. Generally, the composites are prepared by a wet-laid aqueous technique characterized by steps for incorporating a thermoset resin.
Typically, reinforced thermoset materials have been made by hand lay-up methods where the reinforcement is saturated with resin, or resin and solvent and then allowed to dry. The resin saturated material is then arranged into varying shapes as desired and pressed at elevated temperatures to densify and cure the material.
It is desirable to form reinforced thermoset materials in a more efficient manner. A solution is to employ a wet-laid aqueous technique such as employed in the formation of polymeric composites. The preparation of reinforced polymeric composites is disclosed in U.S. Pat. Nos. 4,426,470 and 4,431,696. Additionally, foreign patents disclose the wet-laid aqueous procedures modified to produce polymeric composites. Such patents include U.K. Pat. No. 1,263,812; French Patent Publication No. 2,507,123 and European Patent Office Publication No. 0,039,292-Al.
Problems associated with the wet-laid technique for forming a random-fiber thermoset composite are that steps must be taken to produce a sheet which can be subsequently shaped and/or thermoformed. It is understood that a thermoset is a cured plastic material which is irreversibly hardened by crosslinking whereas thermoplastics can be formed and reformed by the application of heat. Therefore in the preparation of a thermoset composite it is necessary to take steps to prevent the wet mat collected from the aqueous slurry from becoming a rigid thermoset solid prior to fabrication.
The subject methods for forming a random-fiber thermoset composite consider these problems and provide for the preparation of a thermoset composite sheet which can be prepared and fashioned into useful articles of manufacture.